太阳光球层中真的存在长寿的特征吗？II。时间平均制粒图像的对比度
Do Long-Lived Features Really Exist in the Solar Photosphere? II. Contrast of Time-Averaged Granulation Images
摘要：
在四个数据集之间比较了时间平均图像的均方根对比度随平均时间的下降：（1）1993年在La Palma记录的一系列太阳颗粒图像;（2）Rieutord等人（2002）在数值模拟中获得的一系列人工颗粒图像;（3）Steffen及其同事计算的类似系列（见Wedemeyer等人，2004}）;（4）一个随机场与一些参数的典型的颗粒，由Rast（2002）构建。此外，（5）使用时间和空间混洗过程从真实颗粒图像获得图像序列，并且分析作为n的函数的来自该序列的n个图像的平均的对比度。真实颗粒图像的系列（1）表现出比模拟颗粒图像的系列（3）和随机场的系列（4）都慢得多的对比度降低。从某个相对较短的平均时间t开始，序列（3）和（4）中对比度的行为类似于t^{-1/2}统计定律，而混洗序列（5）从n = 2开始遵守n^{-1/2}定律。序列（2）显示出对比度的特别缓慢的下降，这可能归因于模拟中使用的边界条件的特定属性。对比度变化规律的分析之间的比较表明，相当肯定的太阳能颗粒的亮度场包含一个长寿命的组件，这可能与当地持久的黑暗粒间洞和/或准规则结构的存在。随机场（4）成功地再现了真实颗粒的对比度变化规律（Rast，2002）的建议可以被拒绝。
英文摘要：
The decrease in the rms contrast of time-averaged images with the averaging time is compared between four datasets: (1) a series of solar granulation images recorded at La Palma in 1993; (2) a series of artificial granulation images obtained in numerical simulations by Rieutord et al. (2002); (3) a similar series computed by Steffen and his colleagues (see Wedemeyer et al., 2004}); (4) a random field with some parameters typical of the granulation, constructed by Rast (2002). In addition, (5) a sequence of images was obtained from real granulation images using a temporal and spatial shuffling procedure, and the contrast of the average of n images from this sequence as a function of n is analysed. The series (1) of real granulation images exhibits a considerably slower contrast decrease than do both the series (3) of simulated granulation images and the series (4) of random fields. Starting from some relatively short averaging times t, the behaviour of the contrast in series (3) and (4) resembles the t^{-1/2} statistical law, while the shuffled series (5) obeys the n^{-1/2} law from n = 2 on. Series (2) demonstrates a peculiarly slow decline of contrast, which could be attributed to particular properties of the boundary conditions used in the simulations. Comparisons between the analysed contrast-variation laws indicate quite definitely that the brightness field of solar granulation contains a long-lived component, which could be associated with locally persistent dark intergranular holes and/or with the presence of quasi-regular structures. The suggestion that the random field (4) successfully reproduces the contrast-variation law for the real granulation (Rast, 2002) can be declined.
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